Periodic arrays of nano-features, such as a nano-islands, nano-rods, and nano-cavities, are useful as a basis of a variety of nano-devices, including electronic, acoustic, photonic, and magnetic devices. Examples of such devices include quantum dot or single electron transistor array, photonic bandgap structures, non-linear acoustic devices, and ultra-high-density information storage media (e.g., magnetic recording media and phase change recording media).
Conventional photolithography and laser lithography are widely used for the fabrication of periodic arrays of features having a diameter of larger than approximately 50 nanometers (nm). However, arrays of nano-features with a less than 50 nm feature size are difficult to fabricate with known lithography techniques. Specifically, arrays having sub 50 nm nano-features fabricated according to conventional methods generally include interference and noise caused by the interaction between adjacent nano-features.
One conventional fabrication technique involves the use of nanoscale, naturally occurring periodic-structured nano-templates, such as anodized aluminum oxide membranes, as a host for the preparation of a new nano-feature array. Anodized aluminum oxide (AAO) membranes are prepared by anodic oxidation of aluminum metal in an acidic electrolyte such as sulfuric acid, and exhibits a packed, uniform hexagonal array of vertical channels (nano-pores), with the hole diameter of typically 50-500 nm. The diameter and spacing of the nano-pores in AAO depends on certain processing conditions, such as the nature of the anodizing electrolyte used, the anodizing voltage applied, and/or the processing time and temperature.
The AAO membrane has been used as a matrix material to fill the vertical nano-channels with other metals or alloys (e.g., by electrodeposition) for fabrication of many different types of nano-composites and nano-wires. If desired, a selective dissolution of the aluminum oxide matrix by alkaline solution, such as NaOH, may be used to release the metallic nano-wires.
Another conventional approach to nano-feature fabrication involves using a colloidal material comprising a host material (e.g., a surfactant type polymer matrix such as trioctylphosphine oxide or oleic acid) including inorganic nano-particles (e.g., quantum dots or magnetic particles), which self-assembles into a periodic array of nano-particles as the solvent dries. According to this method, the nano-particles are geometrically constrained by the surfactant molecules such that a self-assembled periodic array of nano-particles is formed within the surfactant material.
However, processes such as those involving surfactant-mediated periodic ordering based on the evaporation of carrier solvent (e.g., hexane or octane) in a colloidal mixture including nano-particles (e.g., Co or Fe2O3 nano-particles) and a surfactant (e.g., fatty acids such as oleic acid, oleylamine, hexanoic acid, hexylamine) often suffer from the problem of multiple nucleation and growth of ordering reactions, which leads to non-ordered patterning.
Yet another exemplary nano-structure fabrication technique involves the use of a co-polymer material (e.g., a phase-decomposed and processed diblock copolymer film) as a host material. Nano-pores prepared in the diblock copolymer films may be filled with metals, alloys, or other materials to synthesize nano-composites, nano-islands, and/or nano-wires. The dimension of the ordered nano-pores in the diblock copolymer is generally much smaller than that for the AAO-type membranes.
However, a major drawback to the above-identified techniques is that the periodic arrays of nano-islands or nano-rods that may be formed are often very small in area, e.g., several micrometers. For many electronic, optical, and magnetic products, it is necessary to have a long-range array of periodic elements, on the order of millimeters or centimeters.
For example, according to some conventional fabrication methods, periodically aligned regions nucleate and grow randomly (non-periodically) from numerous locations on a substrate surface, as illustrated in FIG. 1. As shown in FIG. 2, this results in short-range ordered structures having ordered regions formed in discrete domains. As these domains grow, they meet and form boundaries. In this non-periodically arranged structure, these domain boundaries are defective regions, where some of the nano-elements (e.g., nano-islands, nano-particles, and nano-cavities) are mis-registered or missing. As such, short-range ordered structures including an plurality of domains and domain boundaries may not be used in applications that include an array of nano-scale devices, such as, for example, an X-Y array of memory elements or logic elements and/or a nano-patterned magnetic recording media comprising an array of nano-scale devices, for example, an X-Y array of memory elements or logic elements, nano-patterned magnetic recording media. For example, in the case of AAO membranes with an array of vertical holes, each of the domains with near-perfect periodic arrangement are typically only several micrometers in area.
The non-periodic arrangement of such memory devices, logic devices, and/or information bits increases the total number of device defects and reduces the effectiveness and usefulness of the nano-patterned device array. For example, a non-periodic arrangement may cause undesirable electrical shorts, capacitive interactions, noises, and/or interference with neighboring elements. In the case of magnetic hard disc media, undesirable switching or read error of magnetically written bits (magnetized along a desired direction) may occur if the neighboring magnetic islands are spaced too close together when the moving read/write head passes by the magnetic bits to retrieve the written information.
X-Y addressable memories or logic devices desirably contain a periodic array of elements which perform a variety of functions. Some examples of X-Y addressable functions include, for example: i) electrical functions such as in RRAM (resistive random access memory dependent on change of electrical resistance in the elements by X-Y addressing with voltage or current pulses which introduce either amorphous-crystalline phase change or interface electrical resistance change); ii) electric charge-storing functions, e.g., flash memory using storage of electrical charge in floating gate elements; iii) electrical switching functions such as quantum computing quantum dot array, single electron transistor array, and tunnel junction array; iv) optical functions, e.g., magneto-optical memory using laser beam writing/reading in combination with magnetic switching, phase change material with altered optical properties induced by laser pulse heating, or quantum-dot regime luminescent devices; and v) magneto-electric functions, e.g., MRAM (magnetic random access memory). If the elements in the X-Y matrix array of devices are arranged in a non-periodic configuration, the device elements may be mis-registered with respect to the X-Y conductor array lines, causing the device to function in a undesirable manner.
Therefore, there is a need in the art for a method of fabricating a long-range order of periodically arranged nano-features, such as, for example, nano-islands, nano-particles, nano-pores, nano-compositional modifications, and/or nano-device elements).